1. Field of the Invention
This invention relates to a composite with a substrate and a sol-gel layer applied to said substrate as well as a method for the production of the composite.
2. Description of Related Art
In prior art a lot of methods for providing substrates with coatings are known, in particular for incorporating structures to functionalize the substrates. Inter alia, the method of hot stamping is known in which a stamp die is brought into contact with a substrate surface at temperatures which are higher than the softening point of the substrate. In the case of a glass substrate, normally these temperatures are higher than 500° C. This method has the disadvantage that the wear of the forming tool results in high cost. Furthermore, only special substrates having a special melting and solidifying behavior can be used. In addition, the size of the structurable area as well as the plurality of the structures are strongly limited.
Another approach is to provide the substrate with a polymer layer to be structured. Then, the polymer layer may, for example, be structured by means of a stamp die. A substantial disadvantage of such polymer layers is their insufficient thermal stability due to the high portion of organic components. Often, such layers are stable only up to about 100 degrees Celsius (° C.).
Further, there is the method of sol-gel nano-imprint, wherein a stamp die is pressed into a sol-gel layer and subsequently thermal cross-linking is conducted. This method can hardly be used with rigid substrates in large areas. These processes are based on the thixotropic stamping method. In this case a thixotropic lacquer is structured, and the form thus obtained is conserved due to the thixotropic properties of the lacquer. Normally, the fixing action is conducted without contact with a stamp die in a thermal manner or via UV light. The high thixotropic properties of the lacquer are achieved by the addition of respective additives which normally affect the transmittance or the mechanical resistance as well as the pot life of the lacquer.
The stamping of solvent containing thin layer lacquers is also known. In this case, due to the high content of the solvent in the sol most often only layer thicknesses of up to 5 micrometers (μm) can be produced in an industrially realizable production step, due to the sub-optimal network forming and tension crack forming properties in the production of structured thick layers. Also, the produced thick layers are only stable at temperatures of up to about 200° C. respectively show cracks starting with a layer thickness of 5 μm at higher applied load temperatures.
Thus, there is a need for providing composites comprising structurable layers on a substrate which do not show cracks even in the case of higher layer thicknesses. These composites should be producible via an economic process and should have excellent temperature stability. In addition, they should be transparent so that they are suitable for optical applications.